Semiconductor device geometries have dramatically decreased in size since these devices were first introduced several decades ago. Paralleling this development, semiconductor device clock speeds, often measured in terms of frequency, have gone from kilohertz (kHz) to megahertz (MHz) to gigahertz (GHz), requiring electronic signals to travel across device interconnects with increasing speed. As device geometries shrink, and device speeds increase, the need to reduce increased power consumption and signal slowdown due to the RC time delay of the interconnects becomes increasingly important.
Two significant components of the RC time delay in interconnects are the resistance (R) of the conductive material (e.g., a metal such as Al or Cu) used in the interconnect, and the capacitance (C) of the dielectric materials that insulate the interconnect from other conductive regions. Progress has been made on reducing the resistance of the interconnect by, for example, switching from less conductive aluminum to more conductive copper. Progress has also been made on the development of dielectric materials having a lower dielectric capacity (i.e., low-κ materials) to reduce the capacitance side of the RC time delay.
A number of low-κ dielectric materials, and techniques for integrating them into semiconductor devices, have been developed. These include, for example, incorporating fluorine or other halogens (e.g., chlorine, bromine) into a silicon oxide layer. Other low-κ materials include spin-on-dielectrics such as hydrogen silsesquioxane (HSQ), and carbon-silicon containing dielectrics that are deposited by chemical vapor deposition (e.g., plasma CVD), to form silicon-oxygen-carbon (Si—O—C) dielectric films. These materials are often deposited at low temperature (e.g., about 100° C. to about 200° C.) and low density, and often have substantially high porosity.
The high porosity of many of these low-κ dielectric films makes them susceptible to being infiltrated by contaminants in an ambient atmosphere. For example, water vapor (i.e., moisture) can quickly permeate a porous dielectric material and increase the dielectric constant of the layer. In some instances, the increase in κ-value caused by the moisture can make the dielectric layer higher κ than conventional, undoped oxide layers. Thus, there is a need for methods of protecting low-κ dielectric layers from moisture infiltration that increases the dielectric constant of the layers.